The present invention relates to cardiac angiography and more specifically to a method and apparatus for determining the concentration of the iodinated contrast agent in the blood.
Cardiac angiography is an important diagnostic tool, providing high spatial and temporal resolution images of the coronary arteries and cardiac chambers. Angiography is often the definitive test regarding the status of a patient's cardiac anatomy and function. However, one disadvantage of angiography is the projection nature of the images obtained. As a consequence, estimation of the volume of the left ventricle (LV) from angiographic images relies upon a geometric model of the left ventricular chamber. While this technique has been shown to provide accurate LV volumes in many cases, it has also been shown that cardiac disease and dysfunction can result in the LV shape deviating from the assumed shape, resulting in an inaccurate measurement of LV volume. Measurement of left ventricular volume provides important prognostic information regarding several cardiac disease states. It would be desirable to have a technique which provides the LV volume without recourse to an assumption regarding its shape.
Densitometric analysis of digital subtraction angiography (DSA) images can, theoretically, provide such a measurement of LV volume. Ideally, the value of a pixel in a DSA image is given by EQU D=.mu..rho.t
where .mu. is the iodine attenuation coefficient, .rho. is the blood iodine concentration, and t is the thickness of the iodine containing vascular structure at the position of the pixel. One of the problems encountered in making this measurement is the inability to know .rho., the concentration of the iodinated contrast agent in the blood.
It is an object of the present invention to provide a method and apparatus for determining the concentration of iodine in the blood in order to provide an accurate measurement of left ventricle volume.